ART Digital MPATM Microphone Preamplifier TABLE OF CONTENTS Introduction ............................................................................................ 3 Introduction .......................................................................................... 3 Features............................................................................................... 3 Front Panel Controls .............................................................................. 4 Input Gain Control ............................................................................... 4 Input Impedance Control ................................................................. 4-5 Analog Output Control ......................................................................... 5 HPF Control ........................................................................................ 5 Gain Switch ......................................................................................... 5 Phantom Switch ................................................................................... 5 Phase Switch ...................................................................................... 5 Plate Voltage Switch......................................................................... 5-6 Meter Switch........................................................................................ 6 Digital Section Controls ........................................................................ Digital Level Control ............................................................................ Dither Switch ....................................................................................... Sample Rate Control ........................................................................... Optical Switch...................................................................................... 6 6 6 7 8 Front Panel Connections......................................................................... 8 Instrument Inputs................................................................................. 8 Rear Panel Connections......................................................................... 8 Balanced Inputs................................................................................... 8 Balanced Outputs ............................................................................... 8 Insert Jacks ......................................................................................... 9 Word Clock Jacks................................................................................. 9 ADAT Input .......................................................................................... 9 Optical Output....................................................................................... 9 S/PDIF Output ..................................................................................... 9 AES/EBU Output .................................................................................. 9 Signal Path Flow ................................................................................... 10 Signal Path Flow Diagram .................................................................. 10 Operating Instructions ......................................................................... 10 Obtaining the best noise performance ............................................... 10 Adjusting the input impedance...................................................... 10-11 Obtaining the perfect digital level setting ........................................... 11 Setting the tube plate voltage ............................................................ 11 Warranty Information ........................................................................... 12 Service .................................................................................................. 12 Specifications ....................................................................................... 13 2 ART Digital MPATM Microphone Preamplifier DIGITAL MPA INTRODUCTION The ART Digital MPATM microphone preamplifier features a new low noise, high performance preamplification circuitry, designed for superior audio fidelity. Building upon the quality and success of great sounding products like the Pro MPA, ART engineers set out to develop the next generation of professional microphone preamplifier. The Digital MPA is the culmination of years of research and development, and sets a new standard for quality and value. Professional features and spectacular tone are what make the Digital MPA a world-class microphone preamplifier. DIGITAL MPA FEATURES: · · · · · · · · · · · · Variable input impedance for flexible microphone voicing (150 Ohms to 2400 Ohms). Selectable plate voltage Large VU meters Front accessible meter trim Selectable between output level and tube warmth Improved discrete class A input microphone preamplifier Lower noise at low gains Lower THD Wider frequency response Front accessible Instrument Input Jack Very high input impedance Automatically switches to the instrument input when you plug in The Digital MPA also features digital connectivity for use with various digital processors and digital recording devices. The Digital interface supports the following features and functions: · · · · · · · · · · · · · 24-204KHz External sample rate 44.1K, 48K, 88.2K, 96K, 176.4K, 192K Internal sample rates 24/16 bit switchable dithering Wide dynamic range A/D Rotary Encoder for quick selection of sample rate and output format Separate analog and digital output level controls Digital Level LED meters ADAT optical I/O Sync to incoming ADAT data rate Switch selectable optical output (S/PDIF or ADAT) Selectable Pro/consumer output format AES/EBU output on cannon connector Two wordclock jacks allowing loop through ART Digital MPA ­ Rear view image (above) 3 ART Digital MPATM Microphone Preamplifier FRONT PANEL CONTROLS Input Gain Control This control optimizes the input signal level before the tube gain is applied. Both Microphone and Instrument input gains remain the same and are affected by this adjustment. Input gain can be adjusted from 0dB (for line level signals) to 45dB of gain. Use the analog meters in the TUBE setting to gauge how much input gain is required. Additional gain is available via the Gain switch (+20dB) and the Analog Output control (+10dB) for a maximum of 75dB total. The combination of these controls allows the user to adjust the signal level through the tube section, providing more or less "tube" sound as needed. To obtain more "tube' sound, increase input gain, use the +20dB Gain switch, "normal" plate voltage, and less Analog output gain. Both the microphone and instrument inputs are optimized for their respective sources as far as signal levels and noise performance. Running most of the gain on the input generally provides the best performance of the DMPA. Refer to the section titled "Obtaining the best noise performance with the DMPA" for more detailed instructions on setting the Input Gain control for the best results. Input Impedance Control This knob controls the Mic/line input amplifier impedance. This function allows variable voicing of any microphone. Refer to the application section titled "Adjusting the Input Impedance" for more information on making the most of this function. 4 ART Digital MPATM Microphone Preamplifier The 1/4" instrument input is NOT affected by this control, and remains high (>1M Ohm) impedance. Analog Output control The output signal level at the rear output jacks is adjusted by this control. It can provide from +10dB of gain (fully clockwise) to completely muted. You can see the effects of this adjustment reflected in the analog meters when the meter switch is set to "output". HPF control The HPF is a single tuned High Pass Filter that is frequency tunable. The input signal can be filtered to remove "pops" or other extraneous low frequency information. This control moves the rolloff frequency from 10 Hz (fully CCW) to 200 Hz (fully CW). Since it is single tuned (the same as single pole, the simplest kind of filter), it preserves some low frequency content so its use is less obtrusive. It is especially useful in close mic'd applications. Gain switch The Gain switch is used in conjunction with the input gain control to adjust signal levels through the DMPA. When depressed, the tube circuit provides 20dB more gain in the signal path. This also has the effect of driving the tube harder and making the tube the dominant source of gain and overload character. Phantom switch Phantom power on the microphone input is turned on and off with this switch. Depressing the switch will power condenser microphones and other 48volt phantom powered devices. Phantom power is supplied to pins 2 and 3 of the input jack. NOTE: 1) Dynamic microphones are NOT affected by Phantom power, although it should be turned off when using dynamic microphones or line level inputs. 2) Although the 48volt phantom power ramps up and down slowly it may still create a pop. Mute the output of the DMPA when engaging or disengaging phantom power to prevent damage to equipment following the DMPA. Phase switch The Phase switch can invert the phase of the audio signal path in either channel. The Phase switch is located after the tube circuit in the signal path, so you can hear slight differences between different phase selections in the "normal" plate voltage mode near saturation. There are a number of reasons why adjusting the phase is needed these include, wiring errors and inversions in some audio equipment. Some microphones sound different depending on the phase chosen. If two microphones are out of phase, they may cancel at various frequencies (depending on the distance between them). If this happens, try changing the phase of one of the microphones and see if there is an improvement. Plate Voltage switch This switch sets both the tube bias point and the plate voltage level the balanced differential tube circuit runs at. The amount of headroom is adjusted by using the Gain switch and the input Gain 5 ART Digital MPATM Microphone Preamplifier control. The DMPA takes about 10-30 seconds to smoothly transition from one mode to the other. There is a slight increase in gain in the "High" plate voltage mode. In the "normal" (OUT) position, the tube distortion gradually rises until it smoothly clips. The tube is run almost completely open-loop in this mode, providing a musical tube "crunch" when overdriven with a natural recovery from clipping. The tube section can be more easily overdriven when the gain switch is in. This mode brings out the harmonics in the input sources, particularly stringed instruments. The tube circuit runs extremely clean in the "high" (IN) position of the plate voltage switch. As signal levels rise distortion remains very low until within 6dB of clipping, where the overload characteristics smoothly limit the signal swing. There is increased bandwidth (>100KHz), and headroom in this mode as well. Meter Switch The analog meters can monitor either the output signal at the output jacks ("output" position) or the tube output level ("tube" position). VU on the meter measures +4dBu at the output jacks in "output" mode. When in "tube" mode there is 10 to 15dB of headroom above 0VU before the tube saturates (for "normal" and "high" plate voltage settings respectively). Digital Section Front Panel Controls Digital Level Control The levels driving the A/D converter are adjusted with this control. The topology of the DMPA lends itself to simultaneous use of the analog and digital outputs, as each has its' own level control. Common to both is the output signal of the tube circuit. The Digital level control is variable from +10dB to - (fully muted). Located before the Digital level control is the insert jack, allowing processing to be added before digital conversion. As the Digital Level control is used refer to the Digital level LED meter which indicates both peak and average level present at the A/D converter input. This meter helps you get the perfect level adjustment and avoid clipping the A/D. Refer to the section titled "Obtaining the perfect digital level setting" for more detail on the operation and use of these features. Dither Switch The DMPA possesses a 24-bit A/D converter. When the output of the unit goes off to a system that can handle only 16 bit data, the 8 least significant bits of data are ignored (truncated). This leaves the sound with gritty "digital" sounding signals at very low levels. Depressing the Dither switch adds a dither component that when truncated replaces this with a more musical sound as the levels trail off into the noise floor. 6 ART Digital MPATM Microphone Preamplifier Generally, keep the unit in 24-bit mode (the out position of the switch) unless you are connected to a system that will truncate the signal to 16 bits. The 24-bit mode has signific ...